[lldb-dap] Reimplement runInTerminal with signals

runInTerminal is currently implemented using JSON messages over FIFOs,
which feels too clunky for the simple job of passing a PID.

Instead, take advantage of si_pid available from sa_sigaction handler,
and send a user signal instead. Both synchronisation and timeout are
preserved with the protocol below,

1. Debugger waits for SIGUSR1 under timeout with pselect
2. Launcher forks into child, sends SIGUSR1 to debugger and suspends
3. Debugger receives SIGUSR1, captures the sender (launcher child) PID,
   attaches to and resumes it
4. Launcher child resumes and exec's into target
5. Launcher parent waitpid's and kills irresponsive child after timeout

With this, the entirety of FifoFiles and RunInTerminal can be dropped.

Refs: llvm#121269 (comment)

Author: SuibianP

lldb/test/API/tools/lldb-dap/runInTerminal/TestDAP_runInTerminal.py

@@ -14,6 +14,7 @@
 import shutil
 import json
 from threading import Thread
+import signal
 
 
 class TestDAP_runInTerminal(lldbdap_testcase.DAPTestCaseBase):
@@ -30,6 +31,7 @@ def readErrorMessage(self, fifo_file):
             return file.readline()
 
     def isTestSupported(self):
+        return True
         # For some strange reason, this test fails on python3.6
         if not (sys.version_info.major == 3 and sys.version_info.minor >= 7):
             return False
@@ -144,97 +146,21 @@ def test_missingArgInRunInTerminalLauncher(self):
         )
         self.assertNotEqual(proc.returncode, 0)
         self.assertIn(
-            '"--launch-target" requires "--comm-file" to be specified', proc.stderr
+            '"--launch-target" requires "--debugger-pid" to be specified', proc.stderr
         )
 
-    @skipIfWindows
-    @skipIf(oslist=["linux"], archs=no_match(["x86_64"]))
-    def test_FakeAttachedRunInTerminalLauncherWithInvalidProgram(self):
-        if not self.isTestSupported():
-            return
-        comm_file = os.path.join(self.getBuildDir(), "comm-file")
-        os.mkfifo(comm_file)
-
-        proc = subprocess.Popen(
-            [
-                self.lldbDAPExec,
-                "--comm-file",
-                comm_file,
-                "--launch-target",
-                "INVALIDPROGRAM",
-            ],
-            universal_newlines=True,
-            stderr=subprocess.PIPE,
-        )
-
-        self.readPidMessage(comm_file)
-        self.sendDidAttachMessage(comm_file)
-        self.assertIn("No such file or directory", self.readErrorMessage(comm_file))
-
-        _, stderr = proc.communicate()
-        self.assertIn("No such file or directory", stderr)
-
-    @skipIfWindows
-    @skipIf(oslist=["linux"], archs=no_match(["x86_64"]))
-    def test_FakeAttachedRunInTerminalLauncherWithValidProgram(self):
-        if not self.isTestSupported():
-            return
-        comm_file = os.path.join(self.getBuildDir(), "comm-file")
-        os.mkfifo(comm_file)
-
-        proc = subprocess.Popen(
-            [
-                self.lldbDAPExec,
-                "--comm-file",
-                comm_file,
-                "--launch-target",
-                "echo",
-                "foo",
-            ],
-            universal_newlines=True,
-            stdout=subprocess.PIPE,
-        )
-
-        self.readPidMessage(comm_file)
-        self.sendDidAttachMessage(comm_file)
-
-        stdout, _ = proc.communicate()
-        self.assertIn("foo", stdout)
-
-    @skipIfWindows
-    @skipIf(oslist=["linux"], archs=no_match(["x86_64"]))
-    def test_FakeAttachedRunInTerminalLauncherAndCheckEnvironment(self):
-        if not self.isTestSupported():
-            return
-        comm_file = os.path.join(self.getBuildDir(), "comm-file")
-        os.mkfifo(comm_file)
-
-        proc = subprocess.Popen(
-            [self.lldbDAPExec, "--comm-file", comm_file, "--launch-target", "env"],
-            universal_newlines=True,
-            stdout=subprocess.PIPE,
-            env={**os.environ, "FOO": "BAR"},
-        )
-
-        self.readPidMessage(comm_file)
-        self.sendDidAttachMessage(comm_file)
-
-        stdout, _ = proc.communicate()
-        self.assertIn("FOO=BAR", stdout)
-
     @skipIfWindows
     @skipIf(oslist=["linux"], archs=no_match(["x86_64"]))
     def test_NonAttachedRunInTerminalLauncher(self):
         if not self.isTestSupported():
             return
-        comm_file = os.path.join(self.getBuildDir(), "comm-file")
-        os.mkfifo(comm_file)
+        signal.signal(signal.SIGUSR1, signal.SIG_IGN)
 
         proc = subprocess.Popen(
             [
                 self.lldbDAPExec,
-                "--comm-file",
-                comm_file,
+                "--debugger-pid",
+                str(os.getpid()),
                 "--launch-target",
                 "echo",
                 "foo",
@@ -244,7 +170,5 @@ def test_NonAttachedRunInTerminalLauncher(self):
             env={**os.environ, "LLDB_DAP_RIT_TIMEOUT_IN_MS": "1000"},
         )
 
-        self.readPidMessage(comm_file)
-
         _, stderr = proc.communicate()
-        self.assertIn("Timed out trying to get messages from the debug adapter", stderr)
+        self.assertIn("runInTerminal target did not resume in time", stderr)

lldb/tools/lldb-dap/CMakeLists.txt

@@ -14,15 +14,13 @@ add_lldb_library(lldbDAP
   DAPLog.cpp
   EventHelper.cpp
   ExceptionBreakpoint.cpp
-  FifoFiles.cpp
   FunctionBreakpoint.cpp
   InstructionBreakpoint.cpp
   JSONUtils.cpp
   LLDBUtils.cpp
   OutputRedirector.cpp
   ProgressEvent.cpp
   ProtocolUtils.cpp
-  RunInTerminal.cpp
   SourceBreakpoint.cpp
   Transport.cpp
   Variables.cpp